Deep space gravity tests in the solar system

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1 Deep space gravity tests in the solar system Serge REYNAUD Laboratoire Kastler Brossel CNRS, ENS, UPMC (Paris) Discussions and collaborations with persons quoted below and several collaborations Deep Space Gravity Explorer, Hansjörg Dittus (ZARM) et al; Solar System ODYSSEY, Bruno Christophe (ONERA) et al; SAGAS, Peter Wolf (SYRTE) et al; ZACUTO, Orfeu Bertolami (ISTL) et al Investigation of the Pioneer ISSI, Slava G. Turyshev (JPL) et al

2 The scientific context Experimental tests of gravity show a good agreement with General Relativity (GR) But GR is a classical theory which show inconsistencies with quantum field theory ; unification models predict (small) deviations of gravity laws from GR Dark matter and dark energy are seen as gravitational anomalies; as long as they are not also observed through independent means, they may also be interpreted as modifications of gravity laws at large (galactic and cosmic) scales A few measurements in the solar system show deviations from the predictions of GR

3 Tests select GR out of the PPN family GR usually tested against the family of PPN metrics The best test to date : tracking of Cassini during its cruise from Jupiter to Saturn Using also Lunar Laser Ranging Bertotti, Iess, Tortora Nature 425 (2003) Courtesy : NASA

4 Are GR predictions valid at all scales? Fifth-force tests of the Newton law Search for a deviation Exclusion domain in the plane (λ,α) in particular under the form of a Yukawa correction Geophysical Laboratory Windows remain open for deviations at short ranges log 10 α log 10 λ (m) Satellites LLR Planetary or long ranges Courtesy : J. Coy, E. Fischbach, R. Hellings, C. Talmadge, and E. M. Standish (2003) The Search for Non-Newtonian Gravity, E. Fischbach & C. Talmadge (1998)

5 Searches in the short-range window Strong constraint now at sub-mm distances A Yukawa interaction with Newton strength (α=1) must have a range smaller than λ<56µm D.J. Kapner et al PRL 98 (2007) E.G. Adelberger et al, arxiv:hep-ph/ At shorter ranges, tests consist in comparisons of Casimir force measurements with theory Exclusion domain in the plane (λ,α) FIG. 6: Constraints on Yukawa violations of the gravitational 1/r 2 law. The shaded region is excluded at the 95% confidence level. Heavy lines labeled Eöt-Wash 2006, Eöt-Wash 2004, Irvine, Colorado and Stanford show experimental constraints from this work, Refs. [11], [14], [15] and [16, 17], respectively. Lighter lines show various theoretical expectations (Ref. [9]). No deviation reported to date in the short-range window

6 Searches in the long-range window A large-scaled test of gravity was performed by Pioneer 10 & 11 probes during their extended missions decided by NASA after their primary planetary objectives have been met Pioneer 10: pre-launch testing Courtesy : NASA S. Turyshev Pioneer 10/11 as precisely navigated deep-space vehicles : Spin-stabilization and design permitted acceleration sensitivity ~10-10 m/s 2, unlike a Voyager-type 3-axis stabilization that were almost 50 times worse

7 The largest scaled gravity test ever carried out and it failed to confirm the known laws of gravity!

8 The Doppler observable A radio signal is sent from a station on Earth to the probe, sent back (transponded) by the probe, and finally received by a station on Earth : the same for 2-way tracking; another one for 3-way tracking. The observable is the frequency ratio, interpreted as a Doppler velocity υ. It depends on the motion of probes while including relativistic and gravitational effects It must also be corrected for propagation effects, station motions.

9 THE DEEP SPACE GRAVITY PROBE SCIENCE TEAM Anomalous acceleration 1 Hz is equivalent to 65 mm/s velocity Deviation of the observed Doppler velocity from the modeled one varying ~ linearly with time Interpreted as an anomalous acceleration J. Anderson et al, Phys. Rev. D 65 (2002)

10 Can the PA be a metric anomaly? It is unlikely that the equivalence principle be violated at the level of the Pioneer anomaly We keep the description of gravitation as a Riemannian metric theory with motions identified as geodesics But the metric in the solar system could differ from GR solution, leading to modifications of geodesic motions of probes or of propagation of radio-links This defines a phenomenology larger than the PPN framework Modifications producing the anomaly should not affect the agreement of other tests with GR but it could produce correlated anomalies to be looked for on other signals M.-T. Jaekel, S. Reynaud, Classical and Quantum Gravity 23 (2006) 7561

11 The two sectors First possibility : a change of the temporal component of the metric It amounts to a modification of Newton law and is constrained by planetary tests But the deviation could appear only after Jupiter Presentation John Moffat Second possibility : a change of the spatial components of the metric It induces a modification of light propagation and is equivalent to a parameter γ depending on the heliocentric distance It has only a small effect on slow material motions (especially on circular orbits) It produces a Pioneer-like anomaly for probes with radial motions in the outer solar system M.-T. Jaekel, S. Reynaud, Classical and Quantum Gravity 23 (2006) 7561

12 Can it be something else? The anomaly has been registered on the two deep space probes with the best navigation accuracy The two probes were identical and had similar trajectories : one experiment performed twice with the same result Might be an artefact? Satisfactory explanation actively looked for, not yet found A challenge ahead of all of us : Will we be able to solve the discrepancy and show that Pioneer gravity test once more confirmed GR? Or to confirm the existence of a gravity anomaly? Any of these two conclusions will be of great value for fundamental physics, astrophysics and cosmology

13 THE DEEP SPACE GRAVITY PROBE SCIENCE TEAM Recent Pioneer Data Recovery Effort Data used for the analysis of ( ) : Pioneer 10: 11.5 years; distance = AU Pioneer 11: 3.75 years; distance = AU Pioneer data recently recovered (Planetary Society & JPL, NASA) : Telemetry & Doppler data recovered from launch to the last data point Doppler Data now available : Pioneer 10: : ~ 30 years Distance range: 4 87 AU Jupiter encounter ~60,000 data points, ~20GB Maneuvers, spin, initial cond. V. Toth and S. Turyshev, arxiv:gr-qc/ Pioneer 11: : ~ 20 years Distance range: 4 33 AU Jupiter & Saturn encounters ~50,000 data points, ~15GB Maneuvers, spin, initial cond. Ongoing Pioneer data re-analysis is an international effort : teams at work in US, Canada, Germany, France, Italy, Norway More informations on the website Investigation of the Pioneer Anomaly ISSI ; results expected within the next year

14 THE STUDY OF THE PIONEER ANOMALY New solutions for Pioneer 10 &11 data at JPL Improvement of solutions (with respect to the analysis published in PRD 2002) Updated Filter strategy Improved models and improved consistency of non gravitational effects on Pioneer 10 & 11 probes Confirms & updates anomaly estimates in Deep Space solutions Observes variations in stochastic acceleration estimates Detects anomaly during Saturn approach More analysis required Courtesy : NASA S. Turyshev

15 Independent analysis of Pioneer data by the French group Same ODF data, independent software J. Anderson et al, Phys. Rev. D 65 (2002) The presence of the anomaly is once more confirmed (its interpretation is still unknown) Gilles Metris & Philippe Berio (OCA), Agnès Lévy (ONERA), Jean-Michel Courty (LKB) Poster presentation Agnès Lévy Groupe Anomalie Pioneer : OCA, ONERA, LKB, IOTA, SYRTE

16 Deep Space Gravity Proposals After the proposal submitted in 2004 to ESA in response to the Cosmic Vision call, the objective of testing Deep Space Gravity has been recognized by ESA 4 Letters of Intent submitted to ESA on end of March 2007 Deep Space Gravity Explorer (Hansjorg Dittus, Bremen) Solar System ODYSSEY (Bruno Christophe, Chatillon) SAGAS (Peter Wolf, Paris) ZACUTO (Orfeu Bertolami, Lisboa) Now, a common roadmap for all these LoI s with 2 proposals to be submitted on end of June 2007 Presentations One class M proposal Bruno Christophe Peter Wolf One class L proposal

THE ANOMALOUS TRAJECTORIES OF THE PIONEER SPACECRAFT a

THE ANOMALOUS TRAJECTORIES OF THE PIONEER SPACECRAFT a Michael Martin Nieto, John D. Anderson, Philip A. Laing, + Eunice L. Lau, and Slava G. Turyshev Theoretical Division (MS-B285), Los Alamos National